1. Field of the Invention
The present invention relates to systems and methods of monitoring and controlling thickness of laminates.
2. State of the Art
In recent years, workers in the battery art have begun to understand and recognize the advantages of so-called laminate batteries that include solid polymer electrolytes and sheet-like anodes and cathodes. The advantages of such batteries include lower battery weights than conventional batteries that employ liquid electrolytes, longer service life, and relatively high power densities. The advantages of laminate batteries also include relatively high specific energies, and the elimination of the danger associated with batteries containing spillable liquid electrolytes such as acids.
Laminate batteries using polymer electrolytes have been developed which possess good performance characteristics. For example, in U.S. Pat. No. 4,925,751, a laminate battery in which a cathode material formed from a mixture of an active cathodic material (preferably vanadium oxide V.sub.3 O.sub.8 or V.sub.6 OC.sub.13), a conductive filler material (preferably carbon particles or filaments), and an ionically conductive polymer electrolyte material is laminated on a conductive substrate material such as a nickel or copper web or sheet. A layer of polymer electrolyte material is laminated over the laminated layer of cathode material, and an anode material is applied over the laminated layer of polymer electrolyte material. The cathode material is applied on the substrate, and the electrolyte material is applied over the cathode material by conventional coating techniques such as with a doctor blade method or an extrusion method.
The cathode material layer on the substrate, generally has a thickness between 25 and 250 microns. The cathode layer thickness is largely determinative of the discharge rate of the battery. The electrolyte material layer on the cathode is applied in the form of a curable, viscous liquid and forms a layer that is generally between 5 and 50 microns thick. While it is desirable to maintain as thin a layer of electrolyte material over the cathode material as possible so that impedance of the electrolyte layer is minimized, if the surface of the cathode material layer is irregular and contains peaks and valleys, the average mean thickness of the electrolyte material layer must be increased to avoid excessively thin spots in the electrode material layer which may result in battery malfunction or failure.
Battery performance requires that the cathode layer and the electrolyte layer have constant thicknesses, with only very small tolerances being permitted. Further, construction of various battery configurations is greatly facilitated by maintaining constant thickness cathode and electrolyte material layers. It is, therefore, desirable to closely monitor and control the thickness and the smoothness of the cathode material layer and the thickness of the electrolyte material layer.